Processes of chemical nickel plating



D. E. METHENY ETAL 2,819,188

PROCESSES OF CHEMICAL mom. PLATING Jan. 7, 1958 Filed May 18, 1954 kEEkm k r. mmmwm mxt m Si n mmvmg m INVENTORS Dana/d E Mei/zany BY Pau/Ta/mey J 1 Q2 w g WW United States Patent PROCESSES OF CHEMICAL NICKELPLATING Donald E. Metheny, Hammond, Ind., and Paul Talmey,

Barrington, Ill-., assignors to General American TransportationCorporation, Chicago, 11]., a corporation of New York Application May 181954, Serial No. 430,604

11 Claims. (Cl. 117- 130) The present invention relates to processesofchemical nickel plating of catalytic materials; and it is the generalobject of the present invention to provide an improved process of thischaracter, employing an aqueous chemical nickel plating solution of thenickel cation-hypophosphite anion type, which is productive of smootherand brighter and better adhering nickel deposits than have been obtainedheretofore.

The chemical nickel plating of a catalytic materialemploying an aqueouschemical nickel plating bath of the type noted is based upon thecatalytic reduction of nickel cations to metallic nickel and thecorresponding oxidation of hypophosphite anions to phosphite anions withthe evolution of hydrogen gas at the catalytic surface. The reactionstake place when the body of catalytic material is immersed in theplating bath, and the exterior surface of the body of catalytic materialis coated with nickel. The following elements are catalytic for theoxidation of'hypophosphite anions and thus may be directly nickelplated: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium and platinum. The following elements are examples of materialswhich may be nickel plated by virtue of an initial displacement depositof nickel thereon eithen directly or through a galvanic effect: copper,silver, gold, beryllium, germanium, aluminum, carbon, vanadium,molybdenum, tungsten, chromium, selenium, tellurium and uranium. Thefollowing elements are examples of non-catalytic materials whichordinarily may not be nickel plated: bismuth, admium, tin, lead andzinc. The activity of the catalytic materials varies considerably andthe following elements are particularly good catalysts in the chemicalnickel plating bath: iron, cobalt, nickel and palladium. The chemicalnickel plating process is autocatalytic since both the original surfaceof the body being plated and the nickel metal that is deposited on thesurface thereof are catalytic; and the reduction of the nickel cationsto metallic nickel in the plating bath proceeds until all of the nickelcations have been reduced to metallic nickel, in the presence of anexcess of hypophosphite anions, or until all of the hypophosphite anionshave been oxidized to phosphite anions, in the presence of an excess ofnickel cations.

A number of suitable aqueous chemical nickel plating baths of the nickelcation-hypophosphite anion type that may be employed in a chemicalnickel plating process of the character noted are disclosed in U. S.Patent No.

- 2,658,841, granted on November 10, 1953, to Gregoire and ofperformance; and three examples of such aqueous chemical nickel platingbaths may be designated: the malic acid-lactic aci'd-succinate bath, themalic acidglycine bath, and the malic acid-succinate bath.

A typical malic acid-lactic acid-succinate plating bath comprises: anabsolute concentration of hypophosph-ite anions in the range 0.15 to1.20 moles/liter; a ratio between nickel cations and hypophosphiteanions in the range 0.25 to 1.60; an absolute concentration of malicacid anions in the range 0.04 to 0.20 mole/liter; an absoluteconcentration of lactic acid anions in the range 0.04 to 1.00mole/liter; the total quantity of the malic acid anions and the lacticacid anions are sumcient to complex at least of the nickel cations; anabsolute concentration of succinate anions of at least 0.04 mole/ liter;and a pH within the range 4.5 to 7.0.

A typical malic acid-glycine plating bath comprises: an absoluteconcentration of hypophosphite anions in the range 0.15 to 1.20 moles/liter; a ratio between nickel cations and hypophosphite anions in therange 0.25 to 1.60; an absolute concentration of malic acid anionssufficient to complex at least 100% of the nickel cations; and anabsolute concentration of glycine anions of at least 0.04 mole/liter;and a pH within the range 4.5 to 9.5.

A typical malic acid-succinate plating bath comprises: an absoluteconcentration of hypophosphite anions in the range 0.15 to 1.20moles/liter; a ratio between nickel cations and hypophosphlte anions inthe range 0.25 to 1.60; an absolute concentration of malic acid anionssufficient to complex at least 100% of the nickel cations; an absoluteconcentration of succinate anions of at least 0.04 mole/liter; and a pHwithin the range 4.5 to 6.0.

In the formulation of any one of these plating baths, an aqueoussolution is prepared of the ingredients named; the nickel cat-ions maybe derived from nickel chloride, nickel sulfate, etc., or variouscombinations thereof; the hypophosphite anions may be derived fromsodium, potass'ium, etc., hypophosphites, or various combinationsthereof; the other additives are introduced into the bath normally asthe acids, or as the soluble salts thereof, etc.; and the desired pH ofthe bath is established by the eventual introduction thereinto of anacid or a base, as required, hydrochloric or sulfuric acid and sodiumhydroxide being recommended, as a matter of economy and simplicity.

In the compositions of the various plating baths, the terms cation,anion and ion, as employed, include the total quantity of thecorresponding elements that are present in the plating bath; i. e., bohundissociated and dissociated material. In other words, 100%dissociation is assumed when the terms noted are used in connection withmolar ratios and concentrations in the plating bath.

In carrying out a chemical nickel plating process of the characternoted, a bath of the aqueous chemical nickel plating solution is held ina plating chamber at a temperature only slightly 'below the boilingpoint thereof, about 210 F., and the solid body of catalytic material isimmersed therein; whereby the chemical nickel plating reaction takesplace, the exterior surface of the catalytic body being coated with thenickel deposit. Subsequently, the catalytic body is withdrawn from theplating bath after a time interval corresponding to the thickness of thenickel plating upon the surface thereof that is desired.

In the carrying out of this chemical nickel plating process, the depositof nickel that is produced upon the surface of the catalytic body is notalways as bright and smooth as is desired, and occasionally in depositsor c'oating's'having a thickness above 2 or 3 rnils there isencounteredpitting or roughness'that is most objectionable.

Accordingly, it is another object of the invention to provide a chemicalnickel plating process of the character described, that involves animproved step, which positively insures a smooth and bright nickeldeposit, effectively eliminates the occasional pitting and roughness ina relatviely thick deposit or coating, and improves the adhesion of thenickel deposit to the base metal.

The present invention is predicated upon the discovery that bright andsmooth nickel deposits may always be obtained in the chemical nickelplating process, along with effective elimination of the occasionalpitting and rough ness in the relatively thick coatings, by contactingthe surfaces of the catalytic bodies with a light gas in highlydispersed form in the aqueous nickel plating solution, the light gasbeing chemically inert with respect to the plating solution, exhibitinga low surface tension toward the plating solution, and having amolecular Weight that is not greater than that of neon. The phenomenoninvolved is not understood, but it is important to note that the resultsobtained from the dispersion of the inert gases in the platingsolutionvary with the molecular weights thereof, as will be hereinafterdemonstrated.

In any case, the cause or causes of the lack of brightness andsmoothness in the nickel deposits or coatings, as well as the occasionalpitting in the relatively thick deposits, is effectively reduced oreliminated by contacting the catalytic bodies undergoing the platingreaction with the light inert gas, and presumably the action of thelight inert gas upon the surfaces of the catalytic bodies, and

possibly with respect to some surface gases occluded thereon, isentirely mechanical, as no chemical reaction therebetween has beenobserved or detected; and preferably, the light inert gas that isdispersed in the aqueous chemical nickel plating solution comprises:hydrogen, helium,

methane or neon, or mixtures thereof. Hydrogen, the

lightest, is the most desirable; and neon, the heaviest, is the leastdesirable.

Further features of the invention pertain to the particular arrangementofthe steps of the process, whereby the above-outlined and additionaloperating features thereof are attained.

The invention, both as to its organization and principle of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawing, in which the single figure isa diagrammatic illustration of a continuous nickel plating system inwhich the process of the present invention may be carried out.

Referring now to the drawing, the continuous nickel plating system thereillustrated, and suitable for the carrying out of the present process,is essentially of the arrangement disclosed in the copending applicationof Paul Talmey and William J. Crehan, Serial No. 299,784, filed July 19,1952, now Patent No. 2,717,218, granted on September 6, 1955. Moreparticularly, the system fundamentally comprises an upstanding reservoir11, an upstanding plating tank or chamber 12, a condenser 13, a primaryvacuum flash tank 14, a secondary vacuum flash tank 15, a primary steamjet pump 16, a secondary steam jet pump 17, and a mechanical pump 18.The reservoir 11 includes a baflled storage compartment 19 and acommunicating regeneration compartment 20, the regeneration compartment20 being provided with agitator mechanism 21 driven by an associatedelectric motor 22. In the arrangement, the inlet of the pump 18communicates with the upper portion of the storage compartment 19; andthe outlet of the pump 18 communicates with the upper portion of thecondenser 13. The lower portion of the condenser 13 communicates withthe lower portion of the plating tank 12; and the upper portion of theplating tank 12 communicates with the upper portion of the pri maryvacuum flash tank 14. The lower portion of the primary vacuum flash tank14communicates with the upper portion of the secondary vacuum flash tank15; and

the lower portion of the secondary vacuum flash tank 15 communicateswith the upper portion of the regeneration compartment 20. Also, theupper portion of the primary vacuum flash tank 14 communicates with theprimary steam jet pump 16, that is also connected to an associatedsource of high pressure steam, not shown; and the discharge from theprimary steam jet pump 16 communicates with the upper portion of thecondenser 13. Also, the upper portion of the secondary vacuum flash tank15 communicates with the secondary steam jet pump 17, that is alsoconnected to the associated source of high-pressure steam, not shown;and the discharge from the secondary steam jet pump 17 communicates withthe atmosphere. The system contains an aqueous chemical nickel platingsolution of the character previously described; whereby a first portionof the plating solution is stored in the reservoir 11 at a relativelylow temperature well below the boiling point thereof and in a relativelyconcentrated form; while a second portion of the plating solution isheld as a bath in the plating tank or chamber 12 at a relatively hightemperature only slightly below the boiling point thereof and in arelatively dilute form. Preferably, the composition of the platingsolution in the plating tank 12 is that previously set forth anddisclosed in the previously-mentioned Gutzeit, Talmey and Leeapplication.

The system further comprises a bottle or tank 23 containing a lightinert gas under relatively high gauge pressure (hydrogen gas for thepurpose of the present description) and an arrangement for dispersingthe hydrogen gas in the aqueous chemical nickel plating solutioncontained in the plating tank 12. In the system alternative arrangementsare illustrated for achieving the dispersion of the hydrogen gas in theplating solution, the first arrangement including a mixing device 24arranged in the communication between the condenser 13 and the lowerportion of the plating chamber 12, and the second arrangement includinga dispersion plate 25 arranged in the lower portion of the plating tank12 in spaced relation slightly above the bottom wall 26 thereof. Moreparticularly, the bottle 23 is provided with a throttling valve 27 thatcommunicates with a header 28; and the header 28 is connected via acontrol valve 29 to the mixing dcvice 24 and via a control valve 30directly with the space between the diffusion plate 25 and the bottomwall 26. Finally, a rack 32 is carried by the top of the plating chamber12 and receives a number of hooks 33 that are employed for the purposeof suspending or hanging a number of catalytic bodies 34 in platingposition in the plating tank 12 above the dispersion plate 30.

In the operation of the system, the plating solution in the storagecompartment 19 may have a temperature of about 150 F.; while the platingsolution in the plating tank 12 may have a temperature of about 210 F.The plating solution is circulated from the upper portion of the storagecompartment 19 by the pump 18 into the upper portion of the condenser13, wherein it is both heated to the required temperature of about 210F. and diluted to the required concentration by the discharge from theprimary steam jet pump 16. The dilution of the plating solution in thecondenser 13 is achieved not only by the introduction of steamthereinto, but also by the introduction of the water vapor thereintothat is withdrawn from the upper portion of the primary vacuum flashtank 14. The plating solution from the condenser 13 is conducted intothe mixing device 24 and thence into the lower portion of the platingtank 12 above the dispersion plate 25.

When the first arrangement noted is employed for the purpose ofdispersing the gaseous hydrogen into the plating solution, the controlvalve 29 is opened, and the control valve 30 is closed; whereby thegaseous hydrogen from the header 28 enters the mixing device 24 so thatit is dispersed therein into the plating solution entering the lowerportion of the plating tank 12. On the other hand, when the secondarrangement noted is employed for the purpose of dispersing the gaseoushydrogen into the plating:solution, the control valve isclosed and thecontrol valve 30 is opened, whereby the gaseous hydrogen from the header28 is introduced into the space between the diffusion plate 25 and thebottom wall 26, while the plating solution is introduced through themixing device 24 into the lower portion of the plating tank 12. In thelastmentioned case, the gaseous hydrogen admitted into the space betweenthe dispersion plate 25 and the bottom wall 26 is dispersed into theplating solution contained in the plating tank 12 by virtue of theaction of the dispersion plate 25, which, of course, is of perforated orporous structure. In any case, an adequate supply of gaseous hydrogenunder the required gauge pressure is maintained in the header 28 fromthe bottle 23 by virtue of the pressure-reducing action of thethrottling valve 25; and the gaseous hydrogen is thoroughly dispersed inthe plating solution contained in the plating tank 12 employing one ofthe arrangements described above; whereby the plating solution incontact with the catalytic bodies 34 suspended upon the hooks 33 in theplating chamber 12 from the rack 32 has the gaseous hydrogen dispensedtherein. Moreover, rising streams of bubbles of the gaseous hydrogenproceed upwardly, as indicated at 35, from the bodies 34 undergoing theplating reaction and escape from the open top of the plating tank 12;whereby the rising bubbles of the gaseous hydrogen 35 are in sweeping orscrubbing relationship with the surfaces of the bodies 34. The platingsolution from the upper portion of the plating tank 12 is introducedinto the upper portion of the primary vacuum flash tank 14, and iscirculated therefrom into the upper portion of the secondary vacuumflash tank 15, and ultimately back into the upper portion of theregeneration compartment 26. In the primary vacuum flash tank 14, avacuum of about 12" Hg is drawn by the primary steam jet pump 16;whereby water vapor is withdrawn from the contained plating solution, aspreviously noted, so that the plating solution in the primary vacuumflash tank 14 is both correspondingly concentrated" and cooled prior tothe introduction thereof into the secondary vacuum flash tank and in thesecondary vacuum flash-tank 15, a vacuum of about 22" Hg is drawn by thesecondary steamjet pump 17, whereby water vapor is withdrawn therefrom,so that the plating solution in the secondary flash tank 15 is bothcorrespondingly concentrated and cooled prior to the return thereof intothe regeneration compartment 20. The platingsolution'returned into theregeneration compartment may "have a temperature of-about 150 F., aspreviously noted, as a consequence of the tandem cooling effectsproduced in the primary and secondary vacuum flash tanks 14 and 15.Also, the plating solution thus returned-to the regeneration compartment20 is in the relatively concentrated form as a consequence of the tandemconcentrating effects produced in the primary and secondary vacuum flashtanks 14 and 15. Since the dis- 2.

charge of the secondary steam jet pump is to the atmosphere, the watervapor withdrawn from the plating solution in the upper portion of thesecondary vacuum flash tank 15 prevents the build-up of water in thecirculated plating solution; and preferably, the weight of steam introduced into the plating solution in the condenser 13 by the-primarysteam jet pump 16 substantially equals the weight of the water vaporwithdrawn therefrom in the" secondary vacuum flash tank 15 anddischarged to the a-t-mosphereby the secondary steam jet pump 17;thereby maintaining thedesired balance of the water supplied to andextracted from the circulated plating solution.

The catalytic bodies 34 are immersed in the plating bath in the platingchamber 12; whereby the metallic nickel (actually an alloy of nickel andphosphorus having a composition of about-89% to 97% nickel and 11% to 3phosphorus by weight) is deposi'ted upon the surfacesdhereof; 'thebodies 34 being. withdrawn from the plating. bath when the'coatingsthereonareof the desired thickness. In-the plating of the catalyticbodies 34, the

'6 rising streams of bubbles of hydrogen gas, being dispersed in theplating solution, sweep the surfaces of the bodies 34, so that thenickel coatings produced thereon are smooth and bright and free frompits and blemishes, as explained more fully hereinafter.

Incident to the plating of the nickel upon the catalytic bodies 34, theinitial composition of the plating bath is altered by the reduction ofthe nickel cations and the oxidation of the hypophosphite anions, aspreviously noted; and the initial pH of'the bath is reduced, aspreviously explained; whereby it is necessary to regenerate the platingsolution in the regeneration compartment 20 by the addition thereto ofan alkalizing reagent to restore the initial pH thereof and of a nickelsalt and a hypophosphite to restore the initial composition thereof; theingredients thus supplied in the regeneration chamber 20 beingthoroughly dissolved therein by operation of the agitator mechanism 21from the electric motor 22. As a matter of convenience, the addedalkalizing reagent may be derived from an aqueous sodium hydroxide stocksolution; and assuming that the initial bath was formulated utilizingnickel chloride and sodium hypophosphite, the added nickel salt may bederived from an aqueous nickel chloride stock solution and the addedhypophosphite may be derived from an aqueous sodium hypophosphite stocksolution. Of course, the exact initial composition of the platingsolution is not restored, as it is apparent that there is a gradualbuildup therein of sodium cations and chlorine anions, as a result ofthe additions, as well as a gradual build-up of phosphite anions, as aresult of the plating reactions. However, this build-up of the foreigncations and anions named is gradual and of small moment until thephosphite anion concentration builds-up to about 1 mole/liter; wherebythe aqueous plating solution may be employed continuously in the platingsystem throughout the corresponding time interval, provided it isappropriately regenerated, either continuously or periodically, asexplained above.

In connection with the continuous nickel plating process, it is notedthat the articles 34 to be nickel plated, and normally having acatalytic surface, are first properly prepared by mechanical cleaning,degreasing and light pickling, substantially in accordance with standardpractices in electroplating processes, prior to the immersion thereof inthe plating bath in the plating tank 12. For example, in the nickelplating of a steel article, it is cus tomary to clean the rust and millscale from the article, to degrease the article, and then to pickellightly the article in a suitable acid, such as hydrochloric acid.Subsequently, the steel article is removed from the plating tank 12after an appropriate time interval corresponding to the requiredthickness of the nickel coating deposited thereon that is desired; andultimately the steel article is rinsed off with water and is then readyfor use.

In some cases when a nickel coating of two mils or more is sought therehas been some tendency toward the formation of surface discontinuitiesin the nickel deposits. This eiiect results in lack of smoothness andbrightness in the nickel deposits and is occasionally productive of pitsin the relatively thick deposits. This deleterious effect may be readilyreduced or eliminated by the introduction and dispersion into theplating solution of the light inert gas, and presumably the action ofthe light inert gas is entirely mechanical, as no chemi cal reactiontherebetween has been observed or detected.

Specifically, the light gas is chemically inert with respect to theaqueous chemical nickel plating solution (thereby eliminating the use ofsuch active or reactive gases as air, oxygen, ammonia, etc.), exhibits alow surface tension toward the plating solution, has a molecular weightthat is greater than that of neon, and is present in a highly dispersedform in the plating solution; and preferably, the light inert gascomprises-z hydrogen, helium, methane or neon, or mixtures thereof.Possibly,

the fundamental function of the light inert gas is twofold: firstly, theplating bath becomes completely saturated therewith and, secondly, theinterfacial tension between the gas and the plating solution is reduced.In any case, the effect is very dramatic in that smooth and brightnickel deposits are obtained, and the tendency toward pitting in therelatively thick deposits is greatly minimized, or eliminatedaltogether.

Ofr'hand, one might anticipate that a great variety of light inert gasesmight be employed for the present purpose, but extensive experimentationhas proved the facts to be to the contrary. More specifically, hydrogenand helium effect a remarkable increase in brightness and smoothness ofthe nickel deposits, along with the elimination of pitting in therelatively thick nickel deposits (hydrogen, the lighter in Weight, beingmore efiective); and methane and neon (being heavier) efiect a lesser,but nevertheless substantial, increase in brightness and smoothness ofthe nickel deposits, without any noticeable tendency toward theelimination of pitting in the relatively thick deposits; whereas heaviergases, like nitrogen, argon and carbon dioxide, exhibit no substantialbeneficial effects with regard to improving the character of the nickeldeposits in either of the particulars noted, although with nitrogen,having a molecular Weight of 28.02, there is a slightly discernibleimprovement in brightness and smoothness. Accordingly, while the actionof the light inert gas is considered to be mechanical, it must have amolecular weight that is not greater than that of neon, so that it has avery high diffusion rate in the aqueous chemical nickel plating solutionand exhibits a low surface tension with respect thereto, in order toachieve the desired beneficial effects explained above. Thus, while theuseful group of light inert gases in the present process consists ofhydrogen, helium, methane and neon, it will be appreciated that hydrogenand helium are by far the most useful, as these gases achieve both theeffect of increasing the brightness and smoothness of the nickeldeposits and the effect of substantially decreasing or preventingpitting in the relatively thick deposlts.

Another advantage of the process is that the light inert gas sweepingthe plating solution seems to act as a collecting agent to removetherefrom dust or other foreign particles, somewhat in the manner of theremoval of particles in a conventional froth-flotation separationprocess. In any case, this process step is most beneficial in theproduction of nickel deposits upon the catalytic bodies that are smooth,bright and lustrous, along with a considerable reduction in pitting inthe relatively thick deposits.

A further advantage in the process resides in the discovery that thereis a dramatic improvement in the adhesion of the nickel coatings to thecatalytic bodies. As an illustration, it can be readily shown in thelaboratory that if a 4" x1 x 6" cold rolled steel bar is given thestandard preparation previously described, and then placed directly intoa plating bath of the character noted, the pH of which is or greater,the resulting adhesion of the nickel deposit to the steel bar will notbe as great as desired, as demonstrated by the subsequent bending ofthis plated steel bar 180 around a 2" diameter mandrel; whereby some ofthe nickel coating will separate from the steel base material. Now if asimilar piece of cold rolled steel bar is prepared in an identicalmanner, and then placed directly in an identical plating bath, throughwhich hydrogen gas is being bubbled, the resulting coating will not onlybe smooth and bright, and substantially free from pits, as previouslyexplained, but subsequently in an identical bending test the adhesion ofthe nickel deposit to the steel bar will be found to be excellent, therebeing no separation of the nickel coating from the steel base materialincident to the bending of this plated steel bar in the manner noted.Whether the improved adhesion results from the circumstance that thenickel coating is of smoother and brighter character, or from some otherfactor, has not been determined, but the adhesion characteristic isvastly improved, and may be otherwise demonstrated in the laboratory inother and conventional impact and scratch tests.

In a series of tests, the following relatively high pH plating bathswere employed:

Bath N0. 1.-Lactic acid-succinate Nickel sulfate m./l 0.07 Sodiumhypophosphite m./l 0.23 Succinic acid In./l 0.12 Lactic acid m./l 0.21pH 5.5

Adjusted with NaOH and/or H 30 Bath No. 2.Malic acid-glycine Adjustedwith NaOH and/ or H 50 In another series of tests, the followingrelatively low pH plating baths were employed:

Bath N0. 4 .Succinate Nickel sulfate m./l 0.09 Sodium hypophosphite m./l0.23 Sodium succinate m./l 0.06 pH 4.6

Adjusted with NaOH and/ or H Bath N0. 5.--Lactic acid-succinate Nickelsulfate m./l 0.09 Sodium hypophosphite m./l.. 0.23 Lactic acid m./l..0.30 Sodium succinate ..'.m./l 0.12 pH 4.7

Adjusted with NaOH and/ or H 80 Bath No. 6.-Malic acid-lacticacid-succinic acid Nickel sulfate m./l 0.07 Sodium hypophosphite m./l0.23 Malic acid m /1 0.06 Lactic acid -..m./l- 0.21 Succinic acid m./l..0.02 pH 4.5

Adjusted with NaOH and/or H 80 In comparative tests involving each ofthe Baths No. l to No. 6, inclusive, it was verified that the nickeldeposits produced upon properly prepared steel objects were improved toa remarkable degree with respect to brightness and smoothness when thelight inert gas was diffused through the plating solution in the platingchamher during the plating reaction; these tests involving each of thelight inert gases: hydrogen, helium, neon and methane; and also in thesecomparative tests, it was verified that the utilization of the lightinert gases: hydrogen and helium, considerably reduced, or eliminatedaltogether, pitting in the relatively thick deposits.

Another peculiarity was discovered in carrying out these comparativetests in conjunction with the utilization of tellurium as a stabilizingadditive in the aqueous chemical nickel plating bath, in accordance withthe process disclosed. in the copending application Paul' Talmey andGregoire Gutzeit, Serial No. 359,428, filed June 3, 1953, now Patent No.2,762,723, granted on-September 11, 1956. More particularly in theTalmey and Gutzeit application mentioned, there is disclosed a processofchemical nickel plating that involves an aqueous chemical nickelplating bath of the general character described, and further includingas a stabilizing and brightening additive tellurium, either in the formTe or in the form T e the tellurium being present in-the plating bath inabout 0.1 to 10.0 parts per million by weight. Specifically, it wasdiscovered that the nickel deposits containing the tellurium additivepossessed very high adhesion to the base metal objects when the platingswere produced in the manner described above (utilizing hydrogen as thelight inert gas) in conjunction with the low pH plating Baths Nos. 4, 5and 6; whereas, on the other hand, the nickel deposits containing thetellurium additive possessed only moderate adhesion to the base metalobjects when the platings were produced in the manner described above(utilizing hydrogen as the light inert gas) in conjunction with the highpH plating Baths Nos. 1 to 3, inclusive. Accordingly, the presentprocess renders entirely feasible the utilization in the low pH platingBaths Nos. 4 to 6, inclusive, of tellurium, as a stabilizing andbrightening agent; and moreover, in these cases, it appears that theutilization of hydrogen as the light inert gas seems to enhancestability with reference to the inhibiting of the spontaneous formationof black precipitate in the plating bath, the problem of inhibiting thespontaneous formation of black precipitate in the plating bath beingdiscussed in greater detail in the Talmey and Gutzeit applicationmentioned.

The present process may be carried out in an exceedingly simple manneras the amount of the light inert gas that is required is not critical,as only gentle bubbling thereof through the plating bath, withoutturbulence, is required; and as a practical matter it has beendiscovered that for each liter of plating solution in the platingchamber the rate of flow of the light inert gas therethrough may beconveniently established at a value corresponding to the rate of flowWithin the approximate range 20 to 60 mL/min. under standard temperatureand pressure conditions (0 C. and 760 mm. Hg). In any case, thediffusion of the light inert gas through the plating bath is at a verylow rate and the streams of rising bubbles therein comprise a greatnumber of small individual bubbles.

In view of the foregoing, it is apparent that there has been provided animproved chemical nickel plating process that is highly suitable for useon a commercial scale, since it involves only simple manipulative steps,and is positively productive of smooth and bright nickel coatings, alongwith a great reduction of pitting in the relatively thick coatings.

While there has been described what is at present considered to be thepreferred embodiment of the inven tion, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. The process of chemically plating with nickel a solid body ofcatalytic material, which comprises providing a hot aqueous chemicalnickel plating bath of the nickel cation-hypophosphite anion type,injecting a light gas from an external source into said hot plating bathin order to maintain a substantial dispersion of said light gas in saidhot plating bath, said light gas being chemically inert with respect tosaid hot plating bath and having a molecular weight that is not greaterthan that of neon so that it has a high ditfsuion rate in said hotplating bath and a low surface tension with respect thereto, andcontacting said body with said hot plating bath having said substantialdispersion of said light inert gas therein,

. 10 whereby a bright smooth nickel plating is deposited upon thesurface of said body.

2. The process of'chemically plating with nickel a solid body ofcatalytic material, which comprises providing a hot aqueous chemicalnickel plating bath of the nickel cation-hypophosphite anion type,injecting a light gas from an external source into said hot plating bathin order to maintain a substantial dispersion-of said light gas in saidhot plating bath, said light gas being chemically inert with respect tosaid hot plating bath and having a molecular weight that is not greaterthan that of neon so that it has a high diffusion rate in said hotplating bath and a low surface tension withrespect thereto, andimmersing said body in said hot plating bath having said substantialdispersion of said ilght inert gas therein, whereby the surface of saidbody is Wetted-by saidhot plating bath and is swept by bubbles of saidlight inert gas dispersed in said hot plating bath so that a brightsmooth nickel plating is deposited upon the surface of said body.

3. The process of chemically plating with'nickel-asolid body ofcatalytic material, which comprises providinga hot aqueous chemicalnickel plating bath of the'nickel cation-hypophosphite anion type,injecting a light gas from an external source into said hot plating'bathin order to maintain a substantial dispersion of said lightgas in saidhot plating bath, said light gas being chemically inert with respect tosaid hot plating bath and having a molecular weight that is not greaterthan that of neon so that it has a high diffusion rate in said hotplating bath and a low surface tension with respect thereto, circulatingsaid hot plating bath having said substantial dispersion of said lightinert gas therein through a plating chamber by introducing the same intothe lower portion of said plating chamber and by withdrawing the samefrom the upper portion of said plating chamber, and arranging said bodyin said plating chamber so that it is immersed in said hot plating bathhaving said substantial dispersion of said light inert gas therein,whereby the surface of said body is wetted by a rising current of saidhot plating bath and is swept by a rising stream of bubbles of saidlight inert gas dispersed in said rising current of said hot platingbath so that a bright smooth nickel plating is deposited upon thesurface of said body.

4. The process of chemically plating with nickel a solid body ofcatalytic material, which comprises providing a hot aqueous chemicalnickel plating bath of the nickel cation-hypophosphite anion type,circulating said hot plating bath upwardly through a plating chamber byintroducing the same into the lower portion of said plating chamber andby withdrawing the same from the upper portion of said plating chamber,injecting a light gas from an external source into the lower portion ofsaid plating chamber and into said hot plating bath in order to maintaina rising stream of bubbles of said light gas in a rising current of saidhot plating bath in said plating chamber, said light gas beingchemically inert with respect to said hot plating bath and having amolecular weight that is not greater than that of neon so that it has ahigh diffusion rate in said hot plating bath and a low surface tensionwith respect thereto, and arranging said body in said plating chamber sothat it is immersed in said rising current of said hot plating bathhaving said rising stream of bubbles of said light inert gas therein,whereby a bright smooth nickel plating is deposited upon the surface ofsaid body.

5. The process set forth inclaim 1, wherein said light inert gas isselected from the class consisting of hydrogen, helium, methane andneon.

6. The process set forth in claim 1, wherein said light inert gas isselected from the class consisting of hydrogen and helium.

7. The process set forth in claim 1, wherein said light inert gasconsists essentially of hydrogen.

8. The process set forth in claim 1, wherein said light inert gasconsists essentially of helium.

9. The process of chemically plating with nickel a solid body ofcatalytic material, which comprises providing a hot aqueous chemicalnickel plating bath of the nickel cation-hypophosphite anion type,circulating a current of said hot plating bath through a platingchamber, producing a thorough mixing and a substantial dispersion of alight gas in said current of said hot plating bath circulated throughsaid plating chamber by injecting said light gas thereinto from anexternal source, said light gas being chemically inert with respect tosaid hot plating bath and having a molecular weight that is not greaterthan that of neon so that it has a high diffusion rate in said hotplating bath and a low surface tension with respect thereto, and placingsaid body in said plating chamber so that it is immersed in said currentof said hot plating bath having said substantial dispersion of saidlight inert gas therein, whereby the surface of said body is wetted bysaid currentof said hot plating bath and is swept by bubbles of saidlight inert gas dispersed in said current of said hot plating bath sothat a bright smooth nickel plating is deposited upon the surface ofsaid body.

10. The process set forth in claim 9, wherein said light inert gas isinjected into said current of said hot plating hath circulated throughsaid plating chamber at a rate in the approximate range 20 to unitvolumes thereof per minute per liter of said hot plating bath containedin said plating chamber, wherein a unit volume of said light inert gascomprises 0.001 liter thereof at a standard temperature of 0 C. and astandard pressure of 760 mm. Hg.

11. The process of chemically plating with nickel a steel body, whichcomprises providing a hot aqueous chemical nickel plating bath of thenickel cation hypophosphite anion type, injecting hydrogen gas from anexternal source into said hot plating bath in order to maintain asubstantial dispersion of said hydrogen gas in said hot plating bath,and contacting said steel body with said hot plating bath having saidsubstantial dispersion of said hydrogen gas therein, whereby a brightsmooth nickel plating is deposited upon the surface of said steel body.

References Cited in the file of this patent UNITED STATES PATENTS2,658,839 Talmey Nov. 10, 1953 2,658,841 Gutzeit Nov. 10, 1953 2,758,075Swalheim Aug. 7, 1956 FOREIGN PATENTS 370,626 Great Britain Apr. 14,1932

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A SOLID BODY OFCATALYTIC MATERIAL, WHICH COMPRISES PROVIDING A HOT AQUEOUS CHEMICALNICKEL PLATING BATH OF THE NICKEL CATION-HYPOPHOSPHITE ANION TYPE,INJECTING A LIGHT GAS FROM AN EXTERNAL SOURCE INTO SAID HOT PLATING BATHIN ORDER TO MAINTAIN A SUBSTANTIAL DISPERSION OF SAID LIGHT GAS IN SAIDHOT PLATING BATH, SAID LIGHT GAS BEING CHEMICALLY INERT WITH RESPECT TOSAID HOT PLATING BATH AND HAVING A MOLECULAR WEIGHT THAT IS NOT GREATERTHAN THAT OF NEON SO THAT IT HAS A HIGH DIFFSUION RATE IN SAID HOTPLATING BATH AND A LOW SURFACE TENSION WITH RESPECT THERETO, ANDCONTACTING SAID BODY WITH SAID HOT PLATING BATH HAVING SAIDSUBSTANTIALLY DISPERSION OF SAID LIGHT INERT GAS THEREIN, WHEREBY ABRIGHT SMOOTH NICKEL PLATING IS DEPOSITED UPON THE SURFACE OF SAID BODY.